The present invention is directed to a polyurea-containing polyurethane composition useful as a filling material in pneumatic tires and in cracks in highways and concrete structures.
The pneumatic tire is unsurpassed in providing load support with maximum shock absorption for automobiles, trucks, aircraft, lift trucks, dock vehicles, military vehicles, municipal service equipment, golf carts, and the like. This superior performance results from a combination of the properties of the reinforced rubber casing and gas at a proper pressure. However, a major drawback to the use of gas-filled pneumatic tires is the inconvenience and danger posed by the tire being punctured. Tire failure, e.g., blow-outs, can result in human injury and equipment damage. In addition, a slow gas leak-results in improper inflation leading to premature tire wear and increased rolling resistance. Furthermore, in an industrial environment where scrap material is strewn along the floor or roadway, the use of gas-filled pneumatic tires must either be avoided or the debris must be constantly removed.
A variety of solutions designed to prevent or mitigate the puncture of pneumatic tires have been proposed and used. Liners of various types have been provided in the tire or between an inner tube and the tire casing serving to mitigate the effects of a tire casing being punctured. A more prevalent method for overcoming the problem is to convert pneumatic tires to solid or semi-solid composite tires. Such tires have gained a wide acceptance for certain mining, industrial, and construction uses where the added weight, and somewhat inferior dynamic performance, could be tolerated for permanent protection from flat tires.
Until recently, such solid deflation-proof tires have depended on the presence of a foamed elastomer filling. Since the foamed fillings in such tires are easily flexed, the tires have serious disadvantages. For example, excessive heat can build-up within the tire and cause the filler to breakdown during service. Filler breakdown reduces the amount of support provided by the foamed elastomeric material. The reduced support can cause severe casing damage. Moreover, the manufacture of a foamed elastomeric material necessitates that gases be generated in situ. Accordingly, the formation of a foamed filling within a tire casing creates gas volumes and pressures within the tire casing that are undefinable and unpredictable. To control this problem and assure uniformity from tire to tire necessitates expensive factory installation.
Because of the drawbacks of foamed polymers as fillers in pneumatic tires, U.S. Pat. No. Re. 29,890 ("Gomberg") proposed a pneumatic tire in which the casing was filled with an elastomeric material that is free of voids. (The terms "voids" and "void" as used herein denote the cellular formation caused by a foam producing material, e.g., carbon dioxide by-product of an isocyanate-water reaction, freon, or air mixed with the reactants.) Specifically, the elastomeric material was produced in the essential absence of a foam producing material in the reaction zone. Since the elastomeric material has less deflection than foam filled tires, superior heat build-up characteristics were obtained. Additionally, the elastomeric material was found to have a Durometer hardness in the range of about 25-43 on the A Scale. The use to which the pneumatic tire is put determines what is a satisfactory Durometer hardness for the elastomeric filling material. For light uses, e.g., golf carts, a Durometer hardness of up to 5 A is satisfactory. In contrast, for heavy duty industrial uses, e.g., fork lifts, earth movers, etc., a Durometer hardness of at least 20 A is satisfactory.
However, because the elastomeric material entirely fills the tire casing without voids, a significant drawback to the elastomeric material of Gomberg is the resultant very high cost of filling a tire. U.S. Pat. No. 4,683,929 ("Wyman") states that efforts to reduce the cost by diluting the elastomeric material filler material with extender oil can result in a sharp decrease in hardness.
To overcome the deficiency of Gomberg, Wyman added water as a reactant to produce carbon dioxide in the reaction zone, but cured the elastomeric material under conditions whereby the carbon dioxide is dissolved in the elastomeric material to produce a substantially void-free elastomeric filling material.
Wyman states that "as a result of the water reaction, a polyurea-containing polyurethane elastomer is obtained having superior hardness characteristics. Oil can be added while maintaining a Durometer hardness of at least 20 on the A scale. While a polyurea-containing elastomer generally has less oil compatibility on a weight basis than an all-urethane-containing elastomer, because of its very high Durometer hardness, it actually has higher oil compatibility for a particular level of Durometer hardness. In other words, whereas urethane systems can be oil-extended at a useful hardness level, the level of oil extension is limited by large decreases in hardness. On the other hand, elastomer prepared in accordance with [Wyman] can be extended by as much as 50 weight percent with oil and still yield a Durometer hardness of 30; at lower hardness levels, up to 60 weight percent oil can be added without bleeding from the elastomer at room temperature."
Pneumatic tires filled with the elastomeric material of Wyman can potentially suffer from premature failure due to the evolution of carbon dioxide dissolved in the elastomeric filling material.
Accordingly, there is a need for a pneumatic tire filling composition that it is neither subject to premature failure by the evolution of carbon dioxide nor prohibitively expensive.